A system for monitoring a charge rate (a charge remaining amount) of a battery that is mounted on a vehicle employing a motor as a power source and that supplies power to the motor is illustrated in Japanese Unexamined Patent Application Publication No. 2011-82937. In this system, a signal indicating the charge rate of the battery is repeatedly transmitted from the vehicle to the center, the center records the charge rate indicated in the transmitted signals, a cellular phone of a user of the vehicle repeatedly inquires of the center about the charge rate of the battery, and the latest charge rate is displayed on the standby screen of the cellular phone. This enables the user to easily know the latest charge rate in a location remote from the vehicle without having to operate the cellular phone.
In a vehicle including a battery for supplying power to electrical equipment (e.g., an air-conditioning device) mounted on the vehicle (hereinafter referred to as “onboard-equipment battery”) and a generating device for charging the onboard-equipment battery, the maximum charging capacity of the onboard-equipment battery is smaller than that of the power source driving battery. Thus if the above-described system is used, there is a problem in that information indicating the charge rate of the battery is transmitted repeatedly and these transmitting operations consume the battery and reduce the charge rate of the battery.